1. Field of the Invention
This invention relates generally to material dispensing systems, and more particularly to a method and apparatus for depositing a substantially viscous material, such as an adhesive, onto a desired substrate in a predetermined quantity and pattern. Preferably, the adhesive is meltblown onto the substrate by extruding the material from a die and contacting the material with high velocity hot air from one side thereof to break up the adhesive into fine particles and propel the particles in a direction substantially parallel to the direction of the air flow and onto the substrate. Both the material and air flows are preferably provided at the point of impact in a sheet and can be readily adjusted to provide a variety of thicknesses and patterns depending upon the desired application.
2. Description of the Related Art
Meltblowing generally refers to a process which includes contacting viscous material with high velocity hot air as the material exits a nozzle or die. The material is typically is blown onto a collector so as to form a web of material or onto a substrate so as to form a desired coating thereon.
An example of a nozzle or die for meltblowing materials is illustrated in U.S. Pat. No. 5,145,689 which discloses a die having a triangular nosepiece of a predetermined length with a plurality of minute material orifices positioned along the length of the apex of the nosepiece, each orifice extruding a filament of material. Hot air passages are positioned on opposite sides of the apex and along the length of the nosepiece so as to contact the filaments of material as they are dispensed. The air stretches and draws the material by drag forces forming microsized filaments substantially having a continuous cross-section corresponding to the shape of the orifices. In use, a plurality of dies are positioned in tandem and intermittent operation of the dies enables a desired pattern of filaments to be deposited on the substrate.
Such a die, however, does not provide for any adjustability of the material flow. Adjustability is advantageous to vary both the pattern and amount of material emitted.
Additionally, the angle between the air and material flows in the noted patent is selected to prevent break-up of the filaments so that the shape of each filament is maintained as it is deposited on the substrate. Furthermore, to enable complete coverage of the substrate, a large number of closely positioned orifices must be provided which can be difficult to machine and keep from clogging.
It therefore would be desirable to provide a method and apparatus for dispensing a substantially viscous material onto a desired substrate which provides complete, even coverage of the substrate, where the pattern and the amount of material emitted from the apparatus can be readily adjusted to accommodate a variety of applications and which is easy to manufacture and prevent from clogging.